Incidence rate of GRB-host-DLAs

Abstract

We discuss our recent work [1] on the incidence rate of damped Lyα systems associated with the host galaxies of gamma-ray bursts (GRB-host-DLAs) using cosmological SPH simulations. Assuming that the GRB occurrence is correlated with the local star formation rate (SFR), we find that the median N<inf>HI</inf> of GRB-host-DLAs progressively shifts to lower N<inf>HI</inf> values with increasing redshift, and the incidence rate of GRB-host-DLAs with log N<inf>HI</inf>>21.0 decreases rapidly at z≥6. This increases the likelihood of observing the signature of IGM attenuation in GRB afterglows towards higher redshift, because it will not be blocked by the red damping wing of GRB-host-DLAs. This enhances the prospects of using high-z GRBs to probe the reionization of the Universe. The overall incidence rate of GRB-host-DLAs decreases monotonically with increasing redshift, whereas that of QSO-DLAs increases up to z=6. A measurement of the difference between the two incidence rates would enable an estimation of the value of η<inf>GRB</inf> which is the mass fraction of stars that become GRBs for a given amount of star formation. Our predictions can be tested by upcoming high-z GRB missions, including JANUS and SVOM. © 2008 American Institute of Physics.